Most countries all over the world have become more or less dependent in the last decades with regards to the various energy sources to be found in the outer spaces. This dependency is all the more query, as a significant occurrence of the fossil fuels can be found on places, which have been under a burden of conflict for a long time.
Due to the excessive use of the conventional energy carriers, the increase of the carbon dioxide content of the atmosphere can be shown, accompanied by the unfavourable change of the weather together with other glasshouse gases.
As a further environmental problem the amount of certain agricultural and communal and other industrial wastes is increasing, bound unambiguously to the human activities in our age, and the present treatment of said wastes also result in the considerable increase of the amount of glass-gases in addition to other environmental problems. We can say that the continuous increase of the amount of said gases with almost unchanged composition can be interpreted as a renewing raw material accompanying human activity.
In Hungary in the communal waste one can find about 2.5 million tons/year of biodegradable organic waste. About 50% of this is amount is degraded to carbon dioxide and methane in the shoot. It means 800 thousands tons/year of carbon dioxide and 400 thousands tons/year of methane load in the atmosphere. The partially dehydrated (unburnt) waste water sludge load on the soil is 1.5 million tons/year, meaning 90.000 tons/year of carbon dioxide and 50.000 tons/year of methane load in the atmosphere. As a result of the above waste deposition process the equivalent value of the carbon dioxide of the emitted glass-gases in the atmosphere is 10 million tons/year. The yearly amount of solid, organic, biologically non-biodegradable waste of industrial origin delivered to the communal waste depository is also 2.5 million pro year. The ratios are similar in other countries of the world. The manufacture of fuels of biological origin and the production of the corresponding necessary syngas has widely spread all over the world.
Thorough lifecycle analysis (LCA) tests have shown on one hand the energetically negative or in some cases just positive balance of the today used processes, and on the other hand the increasing glasshouse effect related to one unit of utilizable energy considering the used energy and intermediates of the processes. (Raisz-Emmer: Effective Carbon Rate . . . , EMEC7 Brno 2006).
The authors of the FP7(7. framework programme) have presumably recognized this problem, when they announced the subject: 2007.3.2.5. Synthetic biofuels via gasification collaborative.
The syngas production from biomass has been already carried out in several countries, the syngas was used in gas motors for producing electrical or thermal energy (Case Study: 2 MWel biomass gasification plant in Güssing. EC Contract No. NNE5/2002/52:OPET CHP/DH Cluster), or Fischer-Tropsch liquid (Choren Program Freiberg) or in some cases methanol has been prepared. In most of the cases the used biomass is a primary forest product derived from forests considered ready for woodcutting, i.e. raw tree-trunk. This raw material has suppressed the furniture production from wood on the market, the use of plastics has spread instead, the energy investment of which several times exceeds the energy obtained from the burnt/pyrolysed wood.
Syngas producing plants have appeared, which utilize only a small part of the wastes, i.e. the non-selectively collected plastic raw materials (Corenso United Oy Ltd., Finland).
According to WO2007005126 syngas is produced from hydrocarbons, and syngas is then converted to methanol. In US2003158270 a catalytic system is disclosed which can be used at a relatively low temperature and pressure, but the production of syngas is not disclosed.
In the Battelle Columbus gasification system (BAL-Fuels Project, 1997) the formed carbon dioxide is disposed of the system and draught is used, reducing thereby the concentration of the useful components of syngas. Its special tar degrading system requires unnecessary operational and investment costs. HTW technology uses wood as raw material and the gasification system is operated at 27 bar. The oxygen blown into the system is obtained from the air separator, nitrogen is used only for drying. In the course of the HTW process a fluid-bed reactor is used, and the obtained gas mixture strongly contaminated with solid particles and tar vapours, said components can separated by an expensive process.
According to EP 0790291 B1 a thermally pre-treated and/or compressed waste is used and gasification is carried out on a fluid bed reactor at a temperature above 2000° C. When using fluid-bed reactors, the solid particles carried away with the gases, have to be removed requiring an expensive separation. In U.S. Pat. No. 5,104,419 the gasification is carried out with a 60:40-40:60 mixture of oxygen and carbon dioxide in a reactor operated at 800-1000° C., there is no heat utilization from the syngas, but tar and other oily products are formed, which have to be treated and carbon dioxide has to be removed from the system. A common feature of the processes in a fluid bed reactor is that a significant part of the fed solid particles stays in the reactor only sufficient for the pyrolysis and the obtained pyrolysis products as the pyrolysis tar cannot be further degraded or take part in the gasification.
On the basis of their widespread experiences Veba Oil technology has elaborated a process for the preparation of secondary raw materials of communal wastes, suitable for the gasification of the products of the previous procedures, and it includes a cracking process [Redepenning, K.: Valorisation des déchets—faisabilité du recyclage chimique. Informations Chimie, 372. (1995) p. 95-99.]. The plastics depolymerize when heated up to 380° C. Upon cooling the formed vapours, the gases and the condensed material are separated, latter is degraded to an oily and an aqueous layer. The isolated depolymerization makes it possible to remove the obtained hydrogen halides from the halo-containing plastic materials by washing before further processing. In the pyrolysis step pyrolysis takes place in the pyrolysis step based on a 70 years old experience in a modernized rotating oven, whereafter the residual pyrolysis burnt coal is introduced to the gasification system after having ground it to dust. The pyrolysis oil is recycled to the pyrolysis reactor if necessary or used in the gasification system. For the gasification a reactor is used which has been operated for 30 years, delivering 16.000 m3 of syngas. Syngas is prepared in a gasification plant from wastes obtained in the course of pyrolysis and other technologies. Since 1972 in Veba 4 gasification lines have been operated at a capacity of about 60 tons/hour. 16.000 Nm3 syngas are produced in a system of a pressure of 60 bar. The pyrolysing system is not suitable for the treatment of highly humid wastes, the gasification is mainly carried out by using air, and the pressure is high in each unit, requiring plus investment and operation costs and the safety risk is increased.
An international comparison may be based on studying 2004 Gasification Database Gasification Plant Datasheets, summarizing the gasification systems operating and under construction in the year of edition. An important part of the operative processes deals with the gasification of petrol coke of oil industry (Shell development) and another part deals with the gasification of biomass and communal waste. A common element of said processes is the use of a brown coal stabilizer component, increasing significantly the sulphur content of the obtained gas, leading to a considerable increase of investment and operation costs.
In the course of the Green Recycle process the used air contains more than 50% of nitrogen, and tar and oil side products, requiring further equipments for the processing or dangerous wastes/side products are obtained.
According to the Primenergy/PRM process gasification is carried out by using air and the gases leaving the generator contain a significant amount of tar vapours and inert nitrogen being adverse from the point of view of utilization.
According to Community Power BioMAX process also air is fed to the system, but the combustion zone is before the reduction zone. The obtained gases also contain tar vapours and inert nitrogen being adverse from the point of view of utilization. According to the Fluid-Bed Gasifier (EPI, Carbona, MTCI) process a mixture of air and water vapour is blown into the biomass grist forming the fluid-bed. In this process the preparation of the solid material is expensive and may be the source of many mistakes and at the same time the obtained gas contains vapour gases, flue ashes and inert nitrogen being adverse from the point of view of utilization. The FERCO process helps to hold back the solid phase but at the same time the other disadvantages of the fluid processes are maintained.